Transport of Lactate in Rainbow Trout White Muscle

Rainbow trout ( Oncorhynchus rnykiss ) retain the majority of lactate produced during exhaustive exercise within the white muscle. Previous studies have suggested that this retention is partiaiiy via a reuptake of released lactate. The purpose of this work was to study lactate uptake using trout white muscle sarcolemmai vesicles. Through modifications to the original mammalian giant vesicle technique (luel. 199 1 ), trout sarcolemmal vesicles were successfully created and used in transport studies. Results indicate that lactate uptake in trout white muscle is partially through a low-affinity carrier which has a derived Km of 56 mM. Pyruvate partially inhibited lactate uptake at concentrations of 10 and 20 mM of lactate, suggesting involvement of a monocarboxylate carrier. Lactate transport inhibitors. 4-acetoamido-4'-isothiocyanstilbene-2.2'-disu~phonic acid (SITS) and a-cyano4hydroxycinnamate (CHC), were found to stimulate apparent lactate uptake. This is interpreted as an inhibition of subsequent efflux. suggesting thar lactate export from trout white muscle is also carrier mediated.